= About removing cataracts =
 

I have been thinking about the methods talked about in removing the gooey material that causes the problem on the old tubes. I have seen Doug's you tube videos about removing it and then placing the tube, and safety glass back on with little spacers, so the two glass parts never touch...

Here's the question, and sorry if this was already covered, but, Safety glass as it applies to tv's in the days of 21AXP22, seemed to be partly for radiation protection, but in later sets, was it not for glass breakage...?

The way those tubes were constructed, the gooey stuff between both pieces of glass most resembles auto windshield safety glass, where there is a plastic between two pieces of glass, and it keeps the glass from flying all over when it gets hit and broken.....

So for safety sake, when removing cataracts, would it be best practice to put back some type of plastic, or rubber....?

Has anyone ever thought about using shoe-goo, or some rubber cement, or a liquid plastic, kinda like plastic resin, with hardener....?

I know I would not want to experiment on a picture tube, but easily an experiment could be done on two pieces of window glass.....

I know there would be all kinds of problems one could encounter trying to mate the two glass pieces with a liquid between them and not getting any bubbles.....

It was done at the factory somehow.....? Anyone think we should be putting something back in there....?

Or am I wrong, and in those later tubes was it still for radiation, where an addition of the second piece of glass, assuming it had some lead content, is all that we need think about when repairing the cataracts....?

I never thought that any CRT safety glass was meant for radiation protection, but I never looked it up one way or the other to find out.

Likely, the removal of the PVA on our bonded CRTs does reduce the overall safety of the sets, but I am not worried about it personally. When millions of TV sets were sold and treated casually in all types of environments, it probably mattered statistically. Non-bonded CRTs (21FBP22, for example) were always used with what I assume is a separate piece of true safety glass, but then if the faceplate from a 21FJP22 is just ordinary glass, the ultimate "added risk" of a no-longer-bonded tube is, I suppose, that it could implode in such a way that its pieces would also shatter the now-separate faceplate and send those pieces flying outward too. Again, it is not something that I am planning to worry about; I would like to hear the opinions of others.

I read the spec sheet this morning on the 21AXP22 and it specifically mentioned the safety glass as for radiation protection. But the PVA seems to be more suited to hazards of broken glass protection.... Thanks....

OK, thank you for that update.

I know the way many model builders get air bubbles out of silicone or other clear glues is to put the object in a vacuum chamber. But, I don't know where you'd find a vacuum chamber big enough for a CRT.

Plus, many of those glues like silicone and shoe goo are air curing and I don't think the stuff would ever really cure in the center of the CRT face. Besides, they may dry clear, but I'm not sure they'd be considered optically clear.

There are optically clear glues and UV cure glues that might work in this situation, but I'd bet it would costs a bundle for something as big as a CRT face.

Dont know for sure but the PVA may be there so no crud
could get between the glass. Remember cleaning many
safety screens in the olden days. Crap got in no matter how
tight & sealed they were. As far as implosion goes I would think
the glass is non shattering to begin with. PVA may add to
protection but I would guess there is a better chance of
choking to death on a hot dog than having the jug toss
daggers at you.

BTW some day I will put up the story about a tot that got sucked up by a CRT. Was going around back in the late 80's, urban myth ???

73 Zeno:smoke:

Is that the one where the mother goes into the kitchen and hears an explosion and comes out and finds everything in the room was sucked toward the tv and her child was missing?

Ha ! Ha ! !

5 picture tubes in a room couldn't do that if they all broke at once....

I'm curious to know which spec sheet said that the safety glass was providing protection from radiation. I have the RCA and Sylvania specs on the 21AX, and don't recall that being mentioned.
That being said, I did use a radiac meter on my CTC-4 with the 21AX, and found that with a white screen the measurement was .4 millirems per hour. According to our museums resident radiologist, that's a bit high. Not too many folks would be watching a color TV close enough to become sick with radiation poisoning. Wonder what a later glass tube would produce at 25 kilovolts. RCA reduced the second anode to 19.5 in the CTC-5, and 23.5 in subsequent chassis until rectangular and leaded glass envelopes became the norm, I believe. :scratch2:

Ahh, but could 6?

I have a service manual for an Admiral that used a 21AXP22 and it mentions there being measurable radiation at the center of the face. I would have to re-read it to see what it said about the safety glass. I don't see how the PVA could offer much more stopping power for radiation than the glass itself.

In an older thread it was stated that the factory poured in the uncured PVA, which must have been almost water thin (perhaps it was heated?) If you look at these tubes you can see a little stopper at the top.

As for the kid and the "exploding" TV, there are some interesting conspiracy theories and such out there. Search deep, deep into the internet and you will find a forum where it is generally believed that the key to unlimited free energy, something like cold fusion or whatever, lies in a GE color TV that malfunctioned in Chicago back in the 60s.

Yep, that's the story I was thinking of...the GE Color TV. Here's one version of the story that caused quite a stir on VK a few years ago: http://www.videokarma.org/showthread.php?t=145996

You know, GE's slogan used to be "We bring good things to life, and suck nails out of walls."

My beliefs about roundie safety glass (I could be wrong):

1) The reason for the safety glass was to survive a certain strength of impact; it had nothing to do with making the faceplate stronger, but only in preventing it being struck directly
2) I believe the impact resistance had little or nothing to do with the bonded or non-bonded construction, that is the bonded roundies were just depending on the impact resistance of the safety glass the same as with a separate glass
If the above is correct, replacing the bonding material with air will have no significant effect on safety; it will mainly provide a place that could collect dirt.

3) The safety glass may have had something to do with decreasing the radius of scatter in case the tube was imploded, but I don't think so.

Later banded tubes did depend on the banding to strengthen the tube by applying pre-stressing compression. Removing the band from a banded tube is dangerous because it can allow expansive forces to develop under an impact that is too small to reverse the pre-compression when the band is intact. Glass is much weaker under expansion than under compression.

4) Color set safety glass I believe did have some lead content, which could contribute to reducing X-rays in addition to lead in the faceplate

5) The introduction of all-glass color tubes brought the possibility of X radiation off the back as well as the faceplate. Thus the inclusion of lead in the glass and warnings to technicians in some cases to operate with all shields in place.

The attachment is of the last page of a rca 1956 tube manual print for the 21AXP22, and is of the x-ray radiation and the use of 1/4" safety glass, and they only mention x-ray protection.... While small, they do mention it. I'm sure once the words "x-ray radiation" made it into public knowledge some parts of the general public were nuts crazy and would not even go to a store that had a color tv in it.... My Mom would not have color tv for this reason, she even freaked out about the b&w sets, saying they had radiation too..... So for that reason, I'm sure rca at least partly used special safety glass to stop some of that deadly radiation.....

While this front glass would protect the more delicate tube from a direct hit, I think the bonded glass with the PVA was closer to safety auto glass with plastic between the two pieces of glass for strike protection, while the front glass could also have contained lead for radiation.....

I'm just wondering if there is any data to back up any of these ideas I had about the pva tubes...

Think about it - an auto windshield has ambient air pressure on both sides. The plastic is definitely strong, strongly bonded to the glass, and stretchy enough to capture the glass shards (and sometimes even the impacting object - but not if it's moving too fast).

Capturing the flying glass from an implosion seems hopeless, and I don't think the bonding material had the strength to prevent anything flying even if the CRT wasn't under vacuum. Simply an optical sealant, is my guess.

I know that no matter if the set be black and white or color; safety glass or no that television repair training used address x ray radiation. It used to be taught that a tech should never reach over a working set having the face of the c.r.t. close to his chest. This was considered dangerous, so there must be a significant amount of radiation coming out of most all c.r.t. sets. Now the mention of the eventual use of lead may change that some; I don't know, but I always think about that when working on any set.

Also, I know that the whole radiation scare for the viewer more or less came along with color TV for whatever reason(s). As a kid I remember moms always making us back up from the color TV which had some strange attraction that made us want to get as close as possible. They talked of harmful radiation and danger to our eyes.

The early 6BK4 HV regulator tubes (before they were made with lead glass) were known x-ray emitters.

jr

The caution for service techs was because X-radiation damage is cumulative. You would not be harmed significantly by one exposure, but day in and day out would not be so good. Same reason x-ray technicians leave the area to take the picture.

The regulator tube problem was not leaded vs. unleaded glass, but tubes that were constructed crookedly so that the source of x-rays at the anode was not blocked by the metal structure at the bottom of the tube. If a defective regulator was mounted vertically and had no shielding underneath, a kid sitting up close with legs under the set would have his legs in the path of the stray x-rays.

Interesting! But wouldn't the leaded glass envelope for the 6BK4 reduce the X-ray emission regardless? or was the stem/header at the base not leaded glass?
Our family cat got better after the 6BK4 was replaced with a leaded one. :)

jr

As to the front face, bonded or un-bonded there is the protection of x-ray shielding if followed in early interchangeability instructions as well as implosion protection. Even if the front glass is not leaded it would provide protection from "soft" x-rays being emitted as there is that "additional layer". Granted, leaded glass is better I know. The manufacturers' had to ensure precautions from a liability/safety standpoint as well as maintaining interchangeability standards for tube replacement back in the day.

As many of us may have noticed, a curved face for a 21FBP is about twice as thick as a 21FJP. The bonding does make up for some difference though.

I do believe we are plenty safe after doing cataract surgery although I will still maintain my distance!

I know of a retired CRT rebuilder and when he's back in town I'll run have to run this past him.

...

A little info here on this old thread:
http://www.videokarma.org/showthread.php?t=250046
jr

I've got a tube soaking now - Channel master rebuild 21FBP22. Yes. It's got a faceplate - weird, huh?

Anyway, after about 2 (or was it three?) weeks, it's very obviously starting to come apart - the material at the edge has debonded entirely from the glass. Interestingly, it's also become quite brittle (the ambient water temp - mid 50's - might be a factor too?). There's a few inches in the center that are obviously bonded, and I'm pretty sure that after a few more weeks, it'll let go.

It seems the plasticizers get leeched out by the water, and it just lets go from the glass. It's certainly a slow process (maybe warmer water helps?), but it seems to be making progress.

I'm getting really curious as to WHAT this stuff is...

I prefer to do my tube soaks in the summer months!

It's important to have the water at the same temp as the tube to minamize any thermo stress..

Well, it's been at a stable temp for 3 weeks now. At the rate this winter's gone, I don't think it'll ever get hot for the summer :(

I've seen 3DS3 tubes with a lead jacket. In what application do you think they were used?

My retired rebuilder guy used to work for Video Display Corp in Dallas. According to him, the bonded face glass was there for implosion protection more than anything and were not leaded.

video display rebuilt two tube for my and they still strong. I think the guy's name used to be Phill. They were located at Profit Drive. I missed their services. also Louis Stangle from united tuner repair.

Ok - the tube I'm soaking is coming along nicely. The faceplate (but not the tube!) cracked (mechanical stresses from the clothespins being a bit enthusiastically applied), and I pulled most of the pieces off. The remainder is soaking, but water seems to make slow but sure inroads into it.

What the heck is this stuff? After soaking, at ambient temperature (55-60 degrees, it's very brittle and not exactly clear. I'm guessing water leeched out the plasticizers from it. It's about 1/16th inch thick. Along the sheets of stuff I've broken off, they're pockmarked with areas where it decayed in advance.

What causes the decay? Possible hint:This tube came from a water-damaged box. Moisture ingress? But that doesn't explain the decay towards the center. Maybe it's an unstable compound - but I've got two RCA tubes that show virtually no sign of delamination (I think this tube's an RCA, too).

Everyone calls it PVA - have we gotten a confirmation that it actually *is* PVA?

Oh yeah, it burns really sooty and is pretty self sustaining once it gets going. Heat softens it up a lot. I tried acetone - no effect.

Is this stuff perhaps really a silicone of some sort? RTV, maybe?

Used in early '70s GE color sets due to X-ray hysteria. Jacket is lead oxide.

PVA= Poly Vinyl Acetate

Here's another question regarding not reintroducing a bonding material between the tube faceplate and the now-clean "safety glass": If most of you who have performed de-cat procedures don't replace the old PVA with something, but leave an air gap between the two, what's the point of reattaching the old front glass? Is it to maintain the extended radius of the tube face as it was when it left the factory and therefore fit the metal tube mask of the front shroud better or does it really matter in regards to this fit? Otherwise the whole reattachment process seems pointless given that the notion of "safety glass" has been defeated by leaving out the glue that makes safety glass work.

The safety glass still provides a first line of impact resistance, and definitely protects against scratches of the tube itself, which would weaken it. How much strength is added by transferring force through the filler to the tube itself is not clear, but I think it is preferable to have the safety glass with an air gap compared to no safety glass at all.

It does seem likely that the greatest amount of impact resistance is from the tube itself, which is under compression from atmospheric pressure. I believe implosion requires that a sufficient uneven force or tension be developed in some part of the tube.

Not entriely unheard of, but some small rebuilder's didn't even re-install the bonded glass and not wanting to deal with PVA and that whole messy process. I have one such tube that's been installed for many years and I'm not concerned about it "imploding". I do prefer the more original look though, but it does make a sharp picture.

And I've seen (much) later rebuilds that had siliconed the faceplate in place, much as we do today.

Ralph, a 21FBP22 is the same tube, or "bulb" with a different style glass in front and not bonded. I can say that it's safety glass will be thicker over the bonded types though.

A little more to your point though is that the tube will bolt in as there is no "precision tolerance" in it's mounting and look good.

And re-attaching the face does keep that original appearence and protect the "bulb" from getting scratched as mentioned. At least you can replace the front again if you need to and not risk any damage to the tube itself should something happen.

many crt rebuilders left off the safety glass.i think channel master installed them.i dont care for the safety glass myself.some were so thick that it made the picture look out of focus.i have a nos rca hi lite that was never installed.jigged it up and it is awesome.this is being saved for something special like maybe a combo.the glass is slighly tinted and the picture is stunning

Are you thinking about the deliberately etched tubes? They had a texture to diffuse reflections, but it did soften the picture a bit.

I like the non-glare finish of the safety glass on the 21FJP22s, so that is one reason I would always reinstall it on any CRTs that I clean.

My CRT is coming along :) After a few weeks of soaking, I've removed most of the broken faceplate, save for a few pieces.

I took a pealed off piece and experimented. Acetone tends to soften the stuff pretty well. I soaked the remainder of the tube in acetone and this netted the softening of the bonding agent. A putty knife could dig out, and even better, dig between the agent and the glass, breaking the seal. I removed a few large pieces, leaving one piece (which doesn't want to be a team player), stuck to the glass. it's soaking now, and hopefully by tomorrow afternoon it'll have absorbed some acetone and softened to the point where I can get a putty knife in to break the seal and peel it off. Once it's gone, I'll wipe the tube and put it into my Zenith, where it belongs....